1. Technical Field
The present invention relates to a measuring device and a measuring method that use a pulsed electromagnetic wave. Particularly, the present invention relates to a measuring device and a measuring method that perform measurement by detecting a time change in the electric field strength of a pulsed electromagnetic wave.
2. Background Art
Electromagnetic waves that have a frequency of 10 GHz to 10 THz or include components in a wide frequency domain (called terahertz band) including further the frequency domain are collectively called terahertz beam. In particular, spectral devices and imaging devices have been proposed for a time domain in which terahertz pulsed beams (called pulsed terahertz pulsed beam) are used.
These devices are configured to radiate terahertz pulsed beams onto various measurement object samples, such as semiconductors and dielectrics, so that the beams transmit through or are reflected on the measurement object samples. Then, a time change of the electric field strength of the pulsed beams is detected. Thus, electric field strength and phase information in each frequency is acquired by Fourier transform. As a result, it becomes possible to acquire in a non-destructive manner the physicality data of each of the various measurement object samples that cannot be acquired or have been difficult to acquire by a Fourier spectrum device.
In order to acquire information on a sample by use of the terahertz pulsed beams, in addition to a time-domain wave from the samples, a reference time-domain wave is needed. As a reference waveform, in the case of a transmission type, a wave detected without a sample is used. In the case of a reflection type, a wave detected with a mirror deemed to have a reflection ratio of 100% is disposed in place of a sample, is used as a reference waveform. The resultant reference waveform is also subjected to the Fourier transform so as to acquire the amplitude intensity and phase information of an electric field for each wavelength.
Patent document 1 discloses a measuring method that uses a terahertz pulsed beam in a case where a sample is limited to a parallel flat plate. The measuring method uses as a reference signal a reflected pulsed beam that is reflected from an incidence surface of the sample and included in a time-domain wave of the reflected beam. Then, the reflected pulsed beam is detected from the time-domain wave of the reflected beam. The measurement is conducted with a differential signal, as a sample signal, acquired by removing the reflected pulsed beam from the time-domain wave of the reflected beam.